Hydraulic brake apparatus



' Nov.,9, 1937. E. G. CARROLL 2,098,553

HYDRAULIC BRAKE APPARATUS Filed April 16, 1928 7E REM ERMES 75 FoRw/w axane@ @wie (lf/Miei@l Y I n atkoznull Patented Nov. 9, 1937 UNITED STATES PATENT OFFICE HYDRAULIC BRAKE APPARATUS linois Application April 1G, 1928, Serial No. 270,286

17 Claims.

'Ihis invention' relates to a hydraulic brake apparatus. Such brakes are usually applied by means oi' a piston moving in a master cylinder. Usually a port for supplying the operating liq- 5 uid to the interior of the cylinder is located just forward of the normal or inactive position of the piston. When the piston moves forwardly it closes the port, but some of the liquid escapes through this port while the piston is crossing it,

io and in this way there is developed a lost `motion eiect which interferes with the eilective application ol' the brakes tending to make their action tardy and with a diminished pressure for applying them.

One of the dimculties encountered in the use of such hydraulic brake apparatus for automobiles. is that if leakage occurs of the liquid from the brake system, the brakesl are not reliable in their operation. In most four wheel brake syso tems, the master cylinder is connected to all of the brakes so that ifan accident occurs to the apparatus. all of the brakesv are usually inoperative.

In my Patent 1,770,064 issued July 8, 1930 on `2.-, an application 214,330 filed August 20, 1927 and copending with this application, I disclosed arrangements tending to solve the above difliculties.

Another of the disadvantages arising from con- 30 necting all of the' brakes with the master cylin- -der is that the pressure applied to the forward brakes is the same as that applied to the rear brakes and the eiect of this sometimes is that the same actual braking force is delivered at 35 the forward wheels as at the rear wheels. This is now recognized as bad practice in brake operation at high speeds and itis now generally believed that the braking force applied to the forward brakes should never be greater than 40 that applied to the rear brakes.

The general. object of this invention is to provide l a hydraulic brake apparatus which will overcome all of the dimculties referred to above and which will be reliable in operation.

A specic object i's to provide a brake apparatus in which the pressure applied to the forward brakes will be less than that applied to the rear brakes. l

A further object of the invention is to provide t another simple means different from the means disclosed in my said patent for maintaining a supply of operating liquid for the chambers of the master cylinder and to provide a construction which will insure that there will be no 55 loss of pressure for the reasons given above.

(Cl. Gil-54.6)

One of the objects of the invention disclosed in my patent is to construct the parts in such a way that there will be no loss of pressure in the working chamber at the commencement of the braking stroke of the pistons. The invenhereinis to provide in combination with such a structure, a hydraulic brake apparatus which, in operation, will apply the rear brakes a short time in advance of the forward brakes. This is most advantageous because when the forward brakes are applied at about the same instant as the rear brakes, any maladiustment in the apparatus might effect the application of the forward brakes rst. This would tend to produce skidding at the rear of the automobile, particularly if the car were being steered to one side.

A further object of the invention disclosed in my patent is to provide a hydraulic brake apparatus of the type indicated above, in which the pressure system connected to the rear brakes is separated from the pressure system connected to the forwrrd brakes and yet these pressures are maintained balanced and equalized when the master cylinder piston is in released position. Moreover when the brakes are applied the pressures in the two systems are increased proportionately by reason of a floating piston having a limited motion relative to a main piston connected to the operating member.

It is a further object of the invention disclosed herein to provide means for maintaining both of the pistons referred to above so positioned when the brake is released that there is substantially no lost motion in applying the brake.

A further object of the invention is toprovide another simple means diiierent from the means disclosed 4in my patent for maintaining a pressure in such a brake system higher than atmospheric pressure.

It is a further object to combine the above desirable features into an operative practical structure in which the piston positioning device is effective regardless 'of differences in pressure 16 A further object of the invention disclosed on one orboth of said pistons caused by said higher than atmospheric pressures.

Further objects of the invention will appear hereinafter.

`The invention consists of the novel parts and combinations of parts to be described hereinafter, all of which contribute to produce an emcient hydraulic brake apparatus.

A preferred embodiment of the invention is described in the following specification, while the broad scope of the invention is pointed out in the appended claims.

The drawing shows a longitudinal section through a, master cylinder embodying my invention and represents the connections from a reservoir which I prefer to use with the system. The connections to the brakes are also indicated.

Referring more particularly to the parts, I represents a master cylinder. This cylinder is preferably constructed with a chamber 2 of relatively small 'diameter which constitutes a working chamberor working bore for supplying liquid under pressure to the brakes. To the rear of the chamber 2 I provide the master cylinder with a chamber 3 of relatively larger diameter. 'I'hese two chambers are connected by a by-pass 4 having a port I opening through the wall of the chamber 2 just in advance of the inactive position of a piston i that works in the chamber 2.

The chamber 2 is provided with a threaded boss 1 from which a connection may be had to the brakes of the automobile. Sometimes in brake apparatus, such a connection from this point is made to all the wheel brakes. I prefer,`

however, merely to connect it to the rear brakes and to provide another chamber as will be described hereinafter for supplying liquid to the forward brakes. The piston 6 is connected to work in unison with a booster piston 3 to which end these two pistons are attached to a common piston rod l. The booster piston 3 is provided with an adjustable connection Il for connecting it with a. brake pedal not illustrated. such as commonly used on automobiles. These pistons are provided with suitable cup-leathers II. The operating liquid is supplied from a reservoir I2 to a suitable pipe I3 and at the connection of this pipe to the interior of the chamber3 I provide an oriilce Il which is relatively small. My reason for doing this will appear hereinafter.

The reservoir I2 is provided with a tight cover 2l. This cover preferably has automatic means for constantly maintaining pressure above atmosphere in the apparatus. This consists of an expansion pressure chamber in the form of a cylinder 2l carrying a hydraulic piston 21 with cup-leather 23. and urged downwardly by a coil spring. 20 in the upper end of the cylinder and thrusting against the under side of a vented bonnet 33. The piston has a tubular piston rod that is closed above the bonnet by a screw cap 3|.

By removing this cap 3| the oil or other liquid in the system may be replenished from time' to time, and if desired this liquid may be forced in under pressure, thereby forcing the piston 21 part way up in the cylinder 2l and compressing the spring which then maintains a high pressure in the system.

The parts of the apparatus described above can be used in any hydraulic brake system and when so used they will have substantially the following mode of operation: When the brake pedal is depressed and the pistons l and 8 move forward in unison. by reason of the large area of the piston 3, a relatively large quantity of liquid will move out of the forward end of the chamber 3. 'Ihe liquid forced out of the chamber 3 in this way will of course raise the level of the liquid in the reservoir I2. At the same time, by reason of the inertia of the column of liquid in the pipe I3 augmented by the relatively small orifice I4, the forward movement of the piston l will develop and maintain pressure in the liquid. This will prevent any loss of pressure in the chamber 2 as the piston 8 crosses the port I. In this way when the piston l has crossed this port and the real application of pressure at the brakes begins, there will be full pressure in the chamber 2.

The master cylinder is preferably constructed so as to operate the forward brakes with a pressure slightly below the pressure developed in the chamber 2. When this is desired, I provide a forward brake chamber I5 formed at the forward end of the master cylinder in axial alignment with the other two chambers 2 and 3. This chamber II has a threaded bore II or other means for connecting it to the forward brakes. In the chamber Il `a forward brake piston I1 moves. Operating liquid is supplied from a reservoir Il through a pipe Il to the interior of the forward brake chamber Il to a port 20 `in its wall Just forward of the piston I1. 'Ihere is a lost motion connection between the piston rod 3 and the piston I1, that is to say, the piston I1 can slide relatively toward the left on a piston rod as shown in the drawing.

Its movement in the other direction is prevented by a nut 2| mounted on the threaded end of the piston rod. I provide a yielding connection` between the piston rod and the piston I1. This yielding connection is preferably in the form of a coil spring 22 which thrusts against a collar 23 on the piston rod 3.

The mode of operation of the chamber I! cooperating with this piston I1 is substantially as follows: When the brake pedal is applied and pressure is developed in the chamber 2, the piston rod 9 will be advancing toward the right. This will transmit force to the piston I1, partly through the spring 22, and partly by liquid pressure, and the pressure developed in the chamber I I will, during braking, be less than that existing in the chamber 2 for the following reasons. The eil'ective area of the front of the piston l is at least as great as the eii'ective area of fthe forward face of the piston I1. The effective area at the rear of piston I1 is less than the effective area at the front end of that piston. Thus the pressure developed in the chamber I5 at all times except when the front of the rod 2l contacts the face |19, equals the pressure in the chamber 2 multiplied by the relatively small area of the rear face I1 and divided by the relatively large area of the front face thereof, plus the strength of the spring. When the iluid pressures in the chambers are low as when the brakes are released and during the takeup phase of brake application, the spring 22 holds the piston I1 forward at its forward limit of movement.

It may be noted that the area of the forward face of the piston I1 is larger than the area of the rearward face thereof. Assuming the fluid pressures in chambers 2 and II are equal there will be a greater total duid force tending to move the piston i1 rearward than the totaliluid force tending to move it forward because of said larger area at the front. However, unless the diiference in total pressures on said faces is great the spring still holds the piston I1 forward as far as the nut 2I allows, as is shown in the drawing. Howa,oes,ess

ever, ashi'gher braking pressures are developed it mayhappen that with such higher pressures if the iluid pressure in chamber Il approaches the pressures in chamber 2, the excess in4 the total pressure on `the front face of piston I1 over that on the rear face of said piston may increase considerably and become stronger than the force of spring 22.' Then the piston i and nut 2I will move forward relative to thepiston Il and cause a desired increase in the uid pressures in the chamber 2. The fact that the eifective area of the piston I is larger than that of the front of piston I1 cooperates with the floating piston II `to insure that greater braking pressures will be transmitted to the rear brakes than to the front brakes. As the piston i advances it displaces 'liquid in the chamber I due to the fact that the piston I is of larger diameter than the piston t., This develops pressure in the chamber l which is only partially relieved by the open passage Il. In this way pressure is maintained in the liquid in the port l as -the piston l advances across the port lI lwhich communicates with the by-pass I. ing the clearance takeup phase of brake. application, the spring maintains the piston in the same position relative to the rod 8 as is shown in the drawing. This insures a prompt closing of the port 2l. Just as the booster piston l is effective to minimize the loss of liquid through the port I vwhen the brakes are being applied, the spring 22 is eil'ective to minimize loss through the port 2l by insuring the closing of the port 20 at the earliest possible time. As is shown, the spring positions the piston I1 just rearward of the port 2l and holds the piston forward while the brakes are released. The pressure in reservoir I2 due to spring 2l acts on both surfaces of piston I1 and therefore would, but for the spring 22, tend to move `the piston I1 rearwardly due to the largerV area of the forward (right) side of the piston exposed to said pressure. The spring also holds the piston forward during the slack takeup portion of the brakev applying stroke so that the port 2l is quickly covered. After the piston I1 has crossed the port 20 suiilciently to close it, a higher positive pressure will be developed in the chamber Il that will be imparted to the forward brakes.` This piston I1 is provided with a cupleather 24 similar to the cup-leathers II already described. This apparatus may operate under a static head due merely to the elevation of the reservoir I2. In this case the reservoir may be left, open. It is desirable, however, that the apparatus may be operated under the considerably higher pressure provided by the arrangement of the reservoir I2 previously described in order to further minimize the loss of liquid though th ports Il and 20.

In the normal operation of the master cylinder, it will be evident as explained above that the pressure that applies the rear brakes will be developed slightly before the pressure is developed inthe cylinder II and the forward brakes. This is desirable because it prevents any possibility of the forward brakes being applied before the rear brakes. g 'I'he latter should be avoided becauseit tends to produce skidding of the rear end of the car if the forward brakes are suddenly applied.

Another desirable effect of the lost motion connection is that in case the rear brake should become inoperative for any reason, there is still a vslight lost motion in the application of the forward brakes. Thus in the operation of the master cylinder, in case of failure of' the rear brakes when there is no pressure in the cylinder 2, it

will be evident that the ilrst part of the movement of the piston rod 0 will be effected without imparting any `movement to the piston I1 except what movement could bey applied through the slight additional compression of the spring 22.` This spring, however, is a light spring and does not transmit anyffmovement to thecpiston I1 from the rst movement of the piston rod i. In other words, the piston II wouldnot commence to move until the end of the rod seats against the face I'I of the piston I1 that would limit the movement ofthe piston rod toward the right.

But when the brakes are released, by reason of the fact that the two reservoir chambers I2 and Il communicate above, the pressure is equalized in the forward and rear brakes. And if either chamber I2 or Il becomes drained of oil as a consequence of a break in the forward or rear brake pipes, the other chamber will maintain an oil supply for the set of brakes remaining intact. The subject matter of certain claims herein is also shown but is not claimed in Patent 1,770,064 whichwas copending with this application.

It is understood that the embodiment of the invention described herein is only one of the many embodiments this invention may take-and I do not wish to be limited in the practice of the invention, nor in the claims, to the particular embodiment set forth.

I claim: i

1. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combinatlon of a master cylinder having a chamber of a given diameter and a chamber of relatively larger diameter, a pistdnmounted in the smaller chamber and a piston mounted in the larger chamber, andhaving means for connecting the same with the brake-pedal, said pistons being connected to move in unison, an unobstructed by-pass connecting the said chambers, with a port opening through the wall of the smaller chamber at such a point that it is traversed by the smaller piston in its movement, and means for connecting the relatively small chamber to the brakes, the piston in the relatively large chamber operating, when moved forwardly, to maintain the pressure in the sma1ler-chamber while the smaller piston is crossing the said port.

2. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a chamber of a given diameter and a chamber of relatively larger diameter, a piston mounted in the smaller chamber and a piston mounted in the larger chamber, and having means for connecting the same with the brake-pedal, said pistons being connected to move in unison, an unobstructed by-pass connecting the said chambers, including a port in the wall of the smaller chamber positioned at such a point that it is traversed by the smaller piston in its movement, a reservoir for supplying the operating liquid to the said chambers and in con-` stant communication with the chamber of larger diameter, means for connecting the relativelyk small chamber to the brakes, the piston in" the relatively large chamber operating, when moved forwardly, to maintain the pressure in the smaller chamber while the smaller piston is crossing the said port. 4

3. In a hydraulic brake apparatus for applying brakes by the actuation ofy a pedal, the combination of a master cylinder having a chamber of a given diameter and a chamber of relatively larger diameter, a smaller piston mounted in the smaller chamber and a Piston mountedln the larger chamber, and having means for connecting the same with a brake-pedal, said pistons being connected to move in unison, an unobstructed by-pass including a port positioned at such a pointthat it is traversed by the smaller piston in its movement and connecting the said chambers, a reservoir having a relatively small orifice connecting the same with the said chambers for supplying operating liquid thereto, and

l means including a port for connecting the relatively small chamber to the brakes, the larger pistonin the larger chamber and the said smaller piston cooperating, when the pistons are moved forwardly, to develop and maintain pressure in the smaller chamber while the smaller piston is crossing the said first named port.

4. In a hydraulic four wheel brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a rear brake chamber of a given diameter and a booster chamber of relatively larger diameter and having a port leading to said rear brake chamber and an unobstructed passage extending from said port to said booster chamber, a smaller piston mounted in the smaller chamber positioned normally Just rearward of said port and a piston mounted in the booster chamber connected with the brake-pedal to be moved in unison, means for connecting the rear-brake chamber to the rear brakes, said master cylinder having a forward brake chamber in alinement with the first named chambers to connect with the forward brakes, a piston in the last named chamber for operating the forward brakes, and a connection between the first named pistons and the last named piston for actuating the same, the piston in the booster chamber operating, when moved forwardly, to maintain the pressure in the rearbrake chamber while the smaller piston is crossing the said port.

5. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a chamber of given diameter for operating the rear-brakes, and a chamber of relatively larger diameter coaxial with the rst named chamber, a rear-brake piston mounted in the smaller chamber and a booster piston mounted in the large chamber with means for connecting the pistons together and to the brake pedal for operating the same, an unobstructed by-pass connecting the said chambers, and having a port opening through the wall of the smaller chamber, said cylinder having a forward-brake chamber forward of the than the relatively small cylinder for operating the forward brakes, alforward-brake piston movable in the last named chamber, means for supplying the operating liquid to the first named chambers and to the last named chamber, and a yieding connection between the piston in the relatively smaller cylinder and the forward-brake piston operating to retard the development of pressure in the forward-brake chamber,

6. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combination ofv a master cylinder having a rear-brake chamber of a given diameter and a booster chamberof relatively larger diameter coaxial therewith, a rear-brake piston movable in the rearbrake chamber and a booster piston movable in the booster chamber, means for connecting said pistons to move in unison and for connecting the same with the brake-pedal, a by-pass connecting the booster chamber to the rear brake chamber aoeaoss having a port opening through the wall of the rear brake chamber located IJust in advance of the rear brake piston, means for supplying liquid to the said chambers, Asaid cylinder having a forward-brake chamber with means for supplying liquid thereto, a forward-brake piston in said forward brake chamber with a spring connection between the same and the first named pistons operating to retard the development of pressure in the forward brake chamber.

7. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a forward chamber of a given diameter and a rear chamber of relatively larger diameter, a forward piston and a rear piston working in said chambers, respectively, and connected together so as to be moved in unison by the brake pedal, the forward chamber having a connection to the brakes, an unobstructed by-pass from the rear chamber to the forward chamber having a port opening through the wall of the forward chamber located just forward of the forward piston, and means for maintaining said chambers supplied with the operating liquid, the piston in the rear chamber operating, when moved forwardly, to maintain the pressure in the forward chamber asl the forward piston crosses said port.

8. In a hydraulic brake apparatus for applying brakes by the actuation of apedal, the combination of a master cylinder having a forward chamber of a given diameter and a-rear chamber of relatively larger diameter, a forward piston and a rear piston working in said chambers respectively and connected together so as to be moved in unison by the brake pedal, the forward chamber having a connection to the brakes, an unobstructed by-pass from the rear chamber to the forward chamber having a port ,opening through the wall of the forward chamber located just forward of the forward piston, a reservoir for the operating liquid connected with the rear chamber, the piston in the rear chamber operating, when moved forwardly, to maintain the pressure in the forward chamber while the forward piston is crossing the said port.

9. In a hydraulic brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a forward chamber of a givendiameter and a rear chamber of relatively larger diameter, a forward piston and a rear piston working in said chamber respectively and connected together so as to be moved in I unison by the brake pedal, the forward chamber relatively small cylinder, and of smaller diameter having a connection to the brakes, an unobstructed by-pass from the rear chamber to the forward chamber having a port opening through the wall of the forward chamber located just forward of the forward piston, a reservoir having a relatively small orice for supplying operating liquid to the rear chamber, the piston and the rear chamber, when moved forwardly, cooperating with the said relatively small orifice to develop and maintain pressure in the liquid within the chambers and prevent loss of pressurein the forward chamber when the forward piston is moving across the said port. i,

l0. In a hydraulic four-wheel brake apparatus for applying brakes by the actuation of a pedal, the combination of a master cylinder having a forward-brake chamber to connect with the forward brakes and a rear brake chamber to connect with the rear brakes, a piston mounted to move in the rear brake chamber with means for actuating the same by the brake-pedal, a forwardbrake piston mounted to move in the forward brake chamber, a common piston-rod for said pistons, the said forward brake piston having a sliding connection with the said piston rod, and yielding means for imparting the forward movement of the piston rod to the forward brake piston operating to yield and retard the development of pressure in the forward-brake chamber.

11. In a hydraulic four-wheel brake apparatus for applying brakes by the actuation of a pedal, the combination of a mastera cylinder having a forward chamber of a given diameter and a rear chamber of relatively larger diameter, a forward piston and a rear piston working in said chambers respectively and connected together so as to be moved n unison by the brake pedal, the forward chamber having a connection to the forward brakes, a valveless by-pass from the rear chamber to the forward chamber having a port opening through the wall of the forward chamber located just forward of the forward piston, and a reservoir for the fluid with a valveless connection to the rear chamber, the piston in the rear chamber operating when moved forwardly, to maintain pressure in the liquid filling the port from the rear chamber into the forward chamber and prevent loss of pressure in the forward chamf ber.

12. In hydraulic brake apparatus for applying forward brakes and rear brakes, the combination of a master cylinder having spaced inlet ports and having a pressure chamber arranged to communicate with the rear brakes and a pressure chamber arranged to communicate with the forward brakes, a plunger movable in the first named pressure chamber to develop pressure therein, a plunger movable in the second named chamber to develop pressure therein, and a resilient connection between the plungers including also a lost motion connection associated therewith, for resiliently urging said plungers to a position in which each is positioned just rearwardly of one of said inlet ports, the connections serving for operating the second named plunger whereby brake applying pressure is developed for the rear brakes before brake applying pressure is developed for the forward brakes, said lost motion connection being capable, after the lost motion has been taken up, of communicating movement directly from the first named plunger to the second named plunger.

13. In fluid pressure apparatus for applying a plurality of brakes, a source of liquid supply, a master cylinder having a plurality of inlet ports connected to said source and a plurality of outlet ports each leading to one of said brakes. a pair of spaced pistons positioned in said master cylinder, one of which is positioned between a pair of said outlet ports and which has a larger liquid pressure receiving face on one side than on the other, means for exerting a greater than atmospheric pressure on the liquid supplied from said source through said ports to said cylinder and thus acting on said pistons, a lost motion mechanical connection between said pistons, and a spring for resiliently urging said pistons toward a. certain spaced relationship in which each is positioned just rearwardly of one of said inlet ports and for counterbalancing the overbalancing force due to the pressure on the larger face.

14. In fluid pressure apparatus for applying a plurality of brakes, a source of liquid supply, a

master cylinder having a plurality of inlet ports connected to said source and a plurality of outlets each leading to one of said brakes, a pair of spaced pistons positioned in said master cyln inder one of which is positioned between a pair of said outlets, a lost motion mechanical connection between said pistons, and a spring for resiliently urging said pistons toward a certain spaced relationship in which each is positioned just rearwardly of one of said inlet ports.

15. A hydraulic brake system, a master cylinder, a fluid reservoir, and a piston in said fluid reservoir, a resilient mea-ns for urging said piston downward to place the fluid in said reservoir under super-atmospheric pressure, a tube extending through said piston, a stop member secured to said tube for limiting the downward movement of said piston, and a cap secured to the upper end of said tube for closing said upper compartment.

16. In a hydraulic braking system for use in combination with a wheel cylinder, a master cylinder having a brake pressure chamber connected to the Wheel cylinder, and a booster chamber positioned back `of said brake pressure chamber and having a. port formed through a wall thereof into said pressure chamber and leading to said booster chamber and having an unobstructed passage extending from said port to said booster chamber, pistons mounted in both chambers and both connected to the brake pedal to be moved in unison and so that said forward piston may move across said port, means for connecting the pressure chamber to the wheel cylinders, and means comprising the piston in said booster chamber for operating when moved forwardly to maintain the pressure in the pressure chamber while the forward piston is crossing the port.

17. In hydraulic brake apparatus for applying front brakes and rear brakes, the combination of a source of supply of liquid, a master cylinder having a pressure chamber arranged to communicate with the rear brakes and a pressure chamber arranged to communicate with the front brakes and having ports connecting each of said chambers to said source of supply of liquid, a plunger movable in the first named chamber to develop pressure therein and normally positioned just rearwardly of the supply port for said first named chamber, a plunger movable in the second named chamber to develop pressure therein and normally positioned just rearwardly of the supply port for said second named chamber, one of said plungers having faces of unequal area, one of which is acted on by the fluid pressure in one chamber, and the other of which is acted on by the fluid pressure in the other chamber, means for exerting a greater than atmospheric pressure on the liquid in said source and thus on the liquid in said chambers so that said liquid reacts on the plungers in their normal position, and a resilient connection between the plungers including a lost motion bis connection associated therewith, said connec- EUGENE G. CARROLL. 

